Tuesday, December 2, 2008

The open ocean has long been a Black Box for predicting salmon survival. Conditions such as temperature variability and food availability are wild cards that have long confounded biologists and fisheries managers forecasting salmon returns. Now a new system of acoustic listening devices that picks up signals from transmitters implanted into the belly cavities of juvenile salmon and other fish is beginning to shed some light into the Black Box. The Pacific Ocean Shelf Tracking network (POST for short) is a series of underwater receivers placed in lines at various locations around the eastern Pacific from San Fransisco to Southeast Alaska. Currently in Canada listening lines are located on both sides of Vancouver Island including Juan de Fuca Strait, Howe Sound, across northern Georgia Strait, Queen Charlotte Strait and off the northwest tip.

Interesting findings are challenging long held beliefs for scientists and environmentalists alike. Mortality in juvenile salmon was previously thought to be highest in freshwater but results from the POST network are showing up to 40% mortality during the smolts' first few weeks once they enter saltwater. Another controversial finding is that juvenile chinook salmon migrating down the highly dammed Columbia River survived their journey equally or better than young chinook migrating down the dam-free Fraser River. Young 10 centimetre long coho have been clocked at nearly 75 kilometres per day in the rivers and up to 40 kilometres per day in the ocean. That is the equivalent of 200,000 body lengths per day. I would have to swim 350 kilometres in the ocean in one day to match that!

Transmitters implanted in other fish like rockfish, sharks, squid, steelhead, sturgeon, and trout are also revealing some previously unknown information. It was known that sturgeon migrate in and out of saltwater but scientist thought they didn't go far. The POST listening array has tracked green strugeon from the Sacramento River in California congregating off the northern end of Vancouver Island.

One prediction that has already proved true is that this revolutionary real-time system of tracking marine animals will be a real breakthrough.